Going from memory, the 5" is a very basic radio and information center package with manual heat controls. The 8.4" adds climate control, nav and camera capabilities, internet wifi bluetooth, and bigger screen. So I suppose if someone wanted to swap out the HVAC system and add the temp sensors, computer bits, and associated wiring and reflash the truck's computer so that it will use those parts (and whatever I overlooked), it might be theoretically possible to upgrade. Long way to go.
I don't remember if the 5" has an aux input, if so you can plug third party stuff into that and find somewhere to mount it.
I remember a day when you could buy a dash conversion kit and mount a really awesome aftermarket sound system, but all the makers these days seem to be going out of their way to prevent that and force you to buy their own proprietary stuff, which is usually pretty crappy.
